1. Field of the Invention
The present invention relates to a direct-current/alternating current (DC/AC) inverter device, and in particular, relates to an inverter device including a multi-level circuit.
2. Description of the Related Art
In recent years, for example, a solar power generation system has been spread and a power system (hereinafter, referred to simply as “system”) interconnection inverter of a non-insulating type is the mainstream in terms of enhancement of efficiency. For example, Japanese Unexamined Patent Application Publication No. 2006-223009 discloses an inverter device including a multi-level circuit that outputs equal to or more than three voltages in order to generate a sine wave voltage (to input a sine wave current into the system) in the non-insulating inverter.
FIG. 1 in Japanese Unexamined Patent Application Publication No. 2006-223009 discloses the configuration of a five-level inverter in which a series circuit of four capacitors and a series circuit of eight switches are provided between positive and negative electrode terminals of a direct-current power supply, and switches or diodes are connected between connection points of these capacitors and connection points of the switch elements.
A multi-level circuit needs 2(n−1) switches when a level number is assumed to be n. For example, in the case of the five-level inverter as described in Japanese Unexamined Patent Application Publication No. 2006-223009, eight switches in total are needed and each of the switches operates at a carrier frequency. Due to this, it is difficult to reduce switching loss in Japanese Unexamined Patent Application Publication No. 2006-223009.